1. Field of the Invention
This invention relates to a process for the preparation in high yield of a conjugated diene polymer of at least 70% diene. More specifically, it relates to the polymerization of a conjugated diene in a system comprising a trihydrocarbyl aluminum and an alkali metal compound such as a lithium alkoxide.
2. Related Prior Art
One of the present inventors was a co-inventor in a number of polymerization processes described in U.S. Pat. Nos. 3,635,922; 3,644,312; 3,644,313; 3,692,883; 3,718,638; 3,769,267; 3,775,392 and Re. 27,878. For these polymerizations, catalyst systems are described which comprise a combination of an alkali metal or an alkali metal hydrocarbyl compound with an alkali metal hydroxide or alkoxide. The alkali metal or alkali metal hydrocarbyl per se was previously known to be a polymerization initiator for dienes. In these prior cases the alkali metal alkoxide or hydroxide is a modifier for the polymerization effected by the alkali metal or the alkali metal hydrocarbyl compound.
U.S. Pat. No. 3,526,604 shows polymerization systems in which Al trialkyls are used with Group IA and IIA metals and organometal compounds of these metals in which the metal is bonded directly to a carbon atom. In a specific listing of possible combinations of Group IA metals with Al trialkyls, sodium isopropoxide is listed as a possible three component combination with the Na metal and an Al trialkyl. Here again, the isoproxide is being used as a modifier, since the teaching is clear that the Na metal in combination with the Al trialkyl is the polymerization initiator. There is no indication that the combination would initiate polymerization in the absence of the sodium metal.
U.S. Pat. Nos. 2,856,391; 3,294,768 and 3,285,894 each show polymerization of dienes in the presence of the combination of an alkyl lithium and an alkali metal alkoxide. Here again, the alkyl lithium is a known polymerization catalyst and the alkoxide is merely a modifier.
Neither Al trihydrocarbyl compounds by themselves nor alkali metal hydroxides, alkoxides, mercaptides, alkylsulfides and amides by themselves are effective in initiating and propagating polymerization of conjugated dienes.